Torque Testing

Torque and Torsion Testing

Here at Applied Technical Services, we have a broad range of capabilities. Torque or Tension testing is another capability that we possess. The association between tension and torque should be considered carefully, since it is quite hard to specify the variation of conditions of a fastener. The amount of the twisting force necessary to rotate the nut along the bolt threads is known as torque, however tension is the elongation or elasticity of a fastener that provides the holding force of a joint. Fasteners are intended to stretch or give slightly, and elongation is what makes the joints lock together. Torque is an incidental indication of tension, as many components can disturb this association, such as texture of the surface, oils, rubbish, thread series, rust and material type for instance. Almost all tables about the torque/tension relationship that have been established, including ours, are founded by one formula:

Torque Formula for Testing

T = (K D P)/12

The proper torque value to use in a particular application is best achieved by utilizing a torque wrench previously calibrated and a load indicating Skidmore-Wilhelm device to associate the verified torque to the ideal tension.

What is proof load? How is proof load dissimilar from ultimate and yield strength?

All of the following are mechanical properties that aid to define the anticipated tensile strength performance of a precise fastener and can be calculated in units of force. The force is reported in Newtons (N) and/or pound-force (lbf). Because the strength of fasteners is normally great, it is habitually to report these forces in kilonewton (kN) and kilopound-force (klbf). The difference is that one is used for standard measurements (inches) and the other is mostly use for metric measurements (mm).

Applying maximum tensile force to a fastener that the outcome will not show plastic deformation is known as proof load. Proof load yield strength is between 85% - 95% normally. That is to say, the fastener must stay in its elastic area when force is applied up to its proof load. We can define Yield Strength as the tensile force that will produce permanent distortion (most commonly 0.2%) to a specified fastener. The maximum force a fastener must tolerate before rupture is defined as Ultimate Tensile Strength.